Make range sync chain Id sequential (#6868)

Currently, we set the `chain_id` of range sync chains to `u64(hash(target_root, target_slot))`, which results in a long integer.

```
Jan 27 00:43:27.246 DEBG Batch downloaded, chain: 4223372036854775807, awaiting_batches: 0, batch_state: [p,E,E,E,E], blocks: 0, epoch: 0, service: range_sync
```


  Instead, we can use `network_context.next_id()` as we do for all other sync items and get a unique sequential (not too big) integer as id.

```
Jan 27 00:43:27.246 DEBG Batch downloaded, chain: 4, awaiting_batches: 0, batch_state: [p,E,E,E,E], blocks: 0, epoch: 0,  service: range_sync
```

Also, if a specific chain for the same target is retried later, it won't get the same ID so we can more clearly differentiate the logs associated with each attempt.

beacon_node/network/src/sync/range_sync/chain.rs

@@ -15,7 +15,6 @@ use rand::seq::SliceRandom;
 use rand::Rng;
 use slog::{crit, debug, o, warn};
 use std::collections::{btree_map::Entry, BTreeMap, HashSet};
-use std::hash::{Hash, Hasher};
 use strum::IntoStaticStr;
 use types::{Epoch, EthSpec, Hash256, Slot};
 
@@ -56,7 +55,7 @@ pub enum RemoveChain {
 pub struct KeepChain;
 
 /// A chain identifier
-pub type ChainId = u64;
+pub type ChainId = Id;
 pub type BatchId = Epoch;
 
 #[derive(Debug, Copy, Clone, IntoStaticStr)]
@@ -127,14 +126,9 @@ pub enum ChainSyncingState {
 }
 
 impl<T: BeaconChainTypes> SyncingChain<T> {
-    pub fn id(target_root: &Hash256, target_slot: &Slot) -> u64 {
-        let mut hasher = std::collections::hash_map::DefaultHasher::new();
-        (target_root, target_slot).hash(&mut hasher);
-        hasher.finish()
-    }
-
     #[allow(clippy::too_many_arguments)]
     pub fn new(
+        id: Id,
         start_epoch: Epoch,
         target_head_slot: Slot,
         target_head_root: Hash256,
@@ -145,8 +139,6 @@ impl<T: BeaconChainTypes> SyncingChain<T> {
         let mut peers = FnvHashMap::default();
         peers.insert(peer_id, Default::default());
 
-        let id = SyncingChain::<T>::id(&target_head_root, &target_head_slot);
-
         SyncingChain {
             id,
             chain_type,
@@ -165,6 +157,11 @@ impl<T: BeaconChainTypes> SyncingChain<T> {
         }
     }
 
+    /// Returns true if this chain has the same target
+    pub fn has_same_target(&self, target_head_slot: Slot, target_head_root: Hash256) -> bool {
+        self.target_head_slot == target_head_slot && self.target_head_root == target_head_root
+    }
+
     /// Check if the chain has peers from which to process batches.
     pub fn available_peers(&self) -> usize {
         self.peers.len()
@@ -1258,7 +1255,7 @@ impl<T: BeaconChainTypes> slog::KV for SyncingChain<T> {
         serializer: &mut dyn slog::Serializer,
     ) -> slog::Result {
         use slog::Value;
-        serializer.emit_u64("id", self.id)?;
+        serializer.emit_u32("id", self.id)?;
         Value::serialize(&self.start_epoch, record, "from", serializer)?;
         Value::serialize(
             &self.target_head_slot.epoch(T::EthSpec::slots_per_epoch()),

beacon_node/network/src/sync/range_sync/chain_collection.rs

@@ -9,6 +9,7 @@ use crate::metrics;
 use crate::sync::network_context::SyncNetworkContext;
 use beacon_chain::{BeaconChain, BeaconChainTypes};
 use fnv::FnvHashMap;
+use lighthouse_network::service::api_types::Id;
 use lighthouse_network::PeerId;
 use lighthouse_network::SyncInfo;
 use slog::{crit, debug, error};
@@ -29,9 +30,9 @@ const MIN_FINALIZED_CHAIN_PROCESSED_EPOCHS: u64 = 10;
 #[derive(Clone)]
 pub enum RangeSyncState {
     /// A finalized chain is being synced.
-    Finalized(u64),
+    Finalized(Id),
     /// There are no finalized chains and we are syncing one more head chains.
-    Head(SmallVec<[u64; PARALLEL_HEAD_CHAINS]>),
+    Head(SmallVec<[Id; PARALLEL_HEAD_CHAINS]>),
     /// There are no head or finalized chains and no long range sync is in progress.
     Idle,
 }
@@ -74,7 +75,7 @@ impl<T: BeaconChainTypes> ChainCollection<T> {
                 if syncing_id == id {
                     // the finalized chain that was syncing was removed
                     debug_assert!(was_syncing && sync_type == RangeSyncType::Finalized);
-                    let syncing_head_ids: SmallVec<[u64; PARALLEL_HEAD_CHAINS]> = self
+                    let syncing_head_ids: SmallVec<[Id; PARALLEL_HEAD_CHAINS]> = self
                         .head_chains
                         .iter()
                         .filter(|(_id, chain)| chain.is_syncing())
@@ -355,7 +356,7 @@ impl<T: BeaconChainTypes> ChainCollection<T> {
             .collect::<Vec<_>>();
         preferred_ids.sort_unstable();
 
-        let mut syncing_chains = SmallVec::<[u64; PARALLEL_HEAD_CHAINS]>::new();
+        let mut syncing_chains = SmallVec::<[Id; PARALLEL_HEAD_CHAINS]>::new();
         for (_, _, id) in preferred_ids {
             let chain = self.head_chains.get_mut(&id).expect("known chain");
             if syncing_chains.len() < PARALLEL_HEAD_CHAINS {
@@ -465,15 +466,17 @@ impl<T: BeaconChainTypes> ChainCollection<T> {
         sync_type: RangeSyncType,
         network: &mut SyncNetworkContext<T>,
     ) {
-        let id = SyncingChain::<T>::id(&target_head_root, &target_head_slot);
         let collection = if let RangeSyncType::Finalized = sync_type {
             &mut self.finalized_chains
         } else {
             &mut self.head_chains
         };
-        match collection.entry(id) {
-            Entry::Occupied(mut entry) => {
-                let chain = entry.get_mut();
+
+        match collection
+            .iter_mut()
+            .find(|(_, chain)| chain.has_same_target(target_head_slot, target_head_root))
+        {
+            Some((&id, chain)) => {
                 debug!(self.log, "Adding peer to known chain"; "peer_id" => %peer, "sync_type" => ?sync_type, &chain);
                 debug_assert_eq!(chain.target_head_root, target_head_root);
                 debug_assert_eq!(chain.target_head_slot, target_head_slot);
@@ -483,13 +486,16 @@ impl<T: BeaconChainTypes> ChainCollection<T> {
                     } else {
                         error!(self.log, "Chain removed after adding peer"; "chain" => id, "reason" => ?remove_reason);
                     }
-                    let chain = entry.remove();
-                    self.on_chain_removed(&id, chain.is_syncing(), sync_type);
+                    let is_syncing = chain.is_syncing();
+                    collection.remove(&id);
+                    self.on_chain_removed(&id, is_syncing, sync_type);
                 }
             }
-            Entry::Vacant(entry) => {
+            None => {
                 let peer_rpr = peer.to_string();
+                let id = network.next_id();
                 let new_chain = SyncingChain::new(
+                    id,
                     start_epoch,
                     target_head_slot,
                     target_head_root,
@@ -497,9 +503,8 @@ impl<T: BeaconChainTypes> ChainCollection<T> {
                     sync_type.into(),
                     &self.log,
                 );
-                debug_assert_eq!(new_chain.get_id(), id);
                 debug!(self.log, "New chain added to sync"; "peer_id" => peer_rpr, "sync_type" => ?sync_type, &new_chain);
-                entry.insert(new_chain);
+                collection.insert(id, new_chain);
                 metrics::inc_counter_vec(&metrics::SYNCING_CHAINS_ADDED, &[sync_type.as_str()]);
                 self.update_metrics();
             }